This invention generally relates to optical sensors; and more specifically to staring optical sensors having adjustable resolutions.
A staring optical sensor is usually a two-dimensional focal plane mosaic of photodetectors each of which generates an electric current representing the intensity of light incident on a given area of observation, referred to as a pixel, and representing one unit of resolution. Typically, the area behind each photodetector is used for electronic circuitry to amplify and multiplex the detector signal.
The spatial resolution of a staring optical sensor is typically determined by the size and spacing of the detectors on the focal plane of the sensor, in conjunction with the focal length of the sensor optical system. In many circumstances, it is desirable to provide the sensor with the ability to operate at both fine and coarse resolutions. The sensor may be used to observe a wide field of view at a coarse spatial resolution to detect a target of interest, and then, once the target is detected, the sensor may be operated to track the target using a narrower field of view with finer spatial resolution. For instance, many space borne applications involve observing the entire earth with a wide field of view for a target, and then tracking the target with a narrower field of view and a finer resolution.
In many situations, including typical space borne applications, all of the sensor components that affect spatial resolutions are fixed and cannot be changed after launch. The requirement, to simultaneously observe a wide field (coarse resolution) and a narrow field (fine resolution), is normally satisfied either by providing either a single wide field sensor with fine resolution globally, or by providing two sensors, one with global coverage and coarse resolution, and a second, pointable sensor with a narrow field of view and fine resolution. Optical zoom techniques usually can not simultaneously offer wide and narrow field performance and present reliability and costs concerns.
Both of the above-mentioned approaches have disadvantages. On the one hand, the traditional single sensor approach, while offering some design and cost advantages, nevertheless requires a relatively large number of inefficiently utilized detector channels, thus requiring a wide bandwidth data link to handle the resulting large quantity of data. The data processor needed to handle this data must also be oversized. On the other hand, the dual sensor approach is burdened by the added weight and costs of a pointing mechanism and of two separate focal planes, optical systems and signal processors.